[OSM-talk] [tagging] Feature Proposal - RFC - incline up down

Shaun McDonald shaun at shaunmcdonald.me.uk
Sat Aug 22 12:10:21 BST 2009


On 22 Aug 2009, at 11:48, John Smith wrote:

> --- On Sat, 22/8/09, Morten Kjeldgaard <mok at bioxray.au.dk> wrote:
>
>> Not really. There's a lot of elevation data available in the GPS  
>> traces, and since roads where incline=* is relevant are drawn along  
>> GPS traces, it's a matter of exploiting that data value. I'm aware  
>> that the GPS elevation data isn't terribly accurate on an absolute  
>> scale, but when determining inclines we will be making elevation  
>> differences which will decrease the error significantly.
>
> I doubt most GPS traces would be useful for this kind of thing, most  
> vertical GPS data is +/- 10m under the best possible conditions,  
> usually I seem to be +/- 20m most of the time, and it's not a stable  
> 20m diff it jumps about just like GPS positions do.
>
> You'd need a GPS with an altimeter, or a stand alone altimeter, to  
> do this kind of elevation differences to get accuracy better than up/ 
> down.
>
>

Remember at last years osm birthday bash we were beside the Thames  
just above sea level and the 20 GPSs in the group were giving a  
variation of around 200 metres if I remember correctly.

Shaun


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